Recently, there has been a strong demand to reduce carbon dioxide emissions in order to suppress global warming. The automobile industry expects that the introduction of Electric Vehicles (EV) or Hybrid Electric Vehicles (HEV) will lead to a reduction in carbon dioxide emissions. Thus, automobile manufacturers have been vigorously developing a motor driving secondary battery, that is, a battery for driving an electrical motor, such that EV or HEV vehicles can be utilized in a practical manner.
In particular, a lithium-ion secondary battery, which exhibits the highest theoretical energy level among all types of batteries, has been deemed the most suitable motor driving secondary battery. Thus, the lithium-ion secondary battery has been rapidly developed. Generally, the lithium-ion secondary battery is configured such that a cathode and an anode having an active material layer, which is formed by coating an active material with a binder on a collector, are connected via an electrolyte layer. The cathode and anode so connected are contained in a battery case.
For example, Japanese Laid-Open Patent Publication No. (Hei) 8-106897 discloses a technique for improving the binder contained in the active material layer of the electrode. More specifically, the technique taught therein forms a mixture paste by using polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVDF) resin or polyvinylidene chloride (PVDC) resin together as a binder in addition to LiNiO2 and a conductive agent. That technique intends to evenly disperse the PTFE resin in a cathode mixture by using at least two types of resins selected from the above combination as a binder in the active material layer. Further, it seeks to improve the bonding property of a metallic foil (collector) and the active material layer by employing the PVDF resin or PVDC resin.